1. Field of the Invention
The invention relates to a drive system for a water vehicle, in particular for an underwater vehicle such as a submarine or an unmanned underwater vehicle and further relates to a method for operating such a drive system and to a water vehicle having such a drive system.
2. Description of the Related Art
Underwater vehicles, such as submarines, are equipped inter alia with fuel cell systems, by which energy is generated to operate the vehicle. The fuel cell system is supplied with pure hydrogen and oxygen or with gases containing hydrogen or oxygen, which are the operating gases. There are several possibilities of storing the operating gases, hydrogen and oxygen, such as in the form of liquefied gases in cryotanks, in the form of compressed gases in pressure vessels or ad/absorbed on/in a substrate, such as in a metal hydride storage unit.
During operation of a drive system of an underwater vehicle based on the combustion of hydrogen and oxygen, each operating gas is removed, e.g., from an operating gas container, in which it is stored at high pressure, and routed into the fuel cell system. In the fuel cell system, both operating gases react to product water. Remaining, uncombusted residual gases escape from a gas outlet of the fuel cell system and must be disposed of. The disposal can take place in two ways, by releasing either (i) into the atmosphere or the surroundings or (ii) into suitable storage containers. This gas outlet only works if either a sufficient volume is available for the storage container or the surrounding atmosphere absorbs a sufficiently large volume so that the escaping gases are diluted.
However, in the case of an underwater vehicle, the volume is limited. A discharge of the residual gas into the water is also not easily possible, because the residual gas may have to be routed out of the interior of the underwater vehicle against the hydrostatic pressure present on the outside. If the operating pressure of the fuel cell system is not sufficiently large for this to be possible, the residual gas is compressed. Electrically driven machines which, however, consume part of the electrical energy generated in the fuel cell system, are generally used as compressors.